The Effect of Wind and Atmospheric Stability on the Morphology of Volcanic Plumes From Vulcanian Eruptions

Abstract

Volcanic plumes from small and moderate eruptions represent a challenge in the study of plume morphology due to eruption source parameter uncertainties and atmospheric influence. Sakurajima volcano, Japan, features such activity and due to its continuous eruptions in the recent years provides an ideal natural laboratory. A data set of 896 eruptions between 2009 and 2016 with well‐constrained plume heights, estimated erupted mass, and associated atmospheric conditions has been compiled. Plume heights ranged between 1,500 and 5,000 m and mainly developed under stable atmospheric stratification and low background wind speeds. The eruptions presented in the database were used to drive FPLUME, a 1‐D integral volcanic plume model, to study the simulated plume morphology. FPLUME was seen to provide consistent results under stable atmospheric stratification. A method for the real‐time monitoring of erupted mass used in the Sakurajima observatory was seen to provide appropriate first guess estimates for the eruptions, showing agreement with analytical and simulated mass flow rate calculations. Volcanic plumes from Sakurajima show significant influence by the atmospheric environment. The plume scaling parameter (Π) was used to characterize the expected degree of plume bending with results correlating well against modeled plume angles. The vertical wind profile was seen to have a significant impact on the resolved plume. Wind shear characteristics were seen to have a mechanical effect on the plume, aiding or inhibiting bending. Finally, potential issues were identified in simulations under unstable atmospheric conditions as the model either failed to provide a solution or overestimated the plume height.

New Insights Into the Relationship Between Mass Eruption Rate and Volcanic Column Height Based On the IVESPA Data Set

“…Figure 2b shows that 𝐴𝐴 𝐻𝐻 std top decreases with stronger horizontal wind speed 𝐴𝐴 𝑊𝑊 , as expected from laboratory experiments (e.g., Carazzo et al, 2014;Hewett et al, 1971) and a few well-observed eruptions (e.g., Dürig et al, 2022;Poulidis et al, 2019), but that the two variables are not significantly correlated. We also do not detect any influence of relative humidity (Figure 3c), despite model predictions that the atmospheric water vapor entrained into a volcanic plume and the associated latent heat flux should boost 𝐴𝐴 𝐻𝐻top by over 5 km for small-moderate eruptions in a wet tropical atmosphere (e.g., Glaze et al, 1997;Herzog et al, 1998;Woods, 1993).…”

Uncertainty Analysis of the Prediction of Massive Ash Fallout From a Large Explosive Eruption at Sakurajima Volcano

“…Numerous studies have been conducted on the health and safety effects of recurrent eruptions in Sakurajima volcano and its surrounding urban areas on nearby communities. Though most eruptive activities are small to moderate (Poulidis et al., 2019), there have been several historical explosive events, including the strongest eruption in Japan of the 20th century, the Taisho eruption of 1914. This eruption caused catastrophic consequences for the country by releasing approximately 2 km 3 of eruptive materials, affecting both proximal and distal regions.…”

A Computational Methodology for the Calibration of Tephra Transport Nowcasting at Sakurajima Volcano, Japan

“…The vulcanian eruption from Minamidake crater under study occurred during the evening of 16 July 2018: starting at 1538 JST (Japan Standard Time; JST = UTC + 9) it lasted for approximately 5 min, leading to an estimated release of 10 7 kg of tephra, based on geophysical monitoring of the volcano [7,9] (Figure 2a). The reported plume height (H P ) by the Japan Meteorological Agency (JMA) was 4.6 km above the vent and easterly winds led to westwards dispersal of the tephra cloud towards the city of Kagoshima, with tephra sedimentation observed at three disdrometer locations.…”

“…Located on the island of Kyushu in southern Japan (31.58 • N, 130.65 • E, peak height 1117 m; Figure 1a), the volcano has been active since 1955, with a major impact on agriculture of ∼236 billion yen between 1978 and 2017 [5]. Due to its frequent activity [6,7] and to the potential impact on human settlements and activities from large eruptions [8], Sakurajima is one of Japan's most closely monitored volcanoes [5,9].…”